A ring network is a network topology in which each node connects to two other nodes, forming a continuous pathway for signals through each node. Data travels from node to node, with each node along the way handling every packet. Rings can be unidirectional (e.g., with the traffic travelling either clockwise or counterclockwise around the ring) or bidirectional (e.g., using Synchronous optical networking (SONET) and synchronous digital hierarchy (SDH)). SONET/SDH are standardized protocols that transfer multiple digital bit streams synchronously over optical fiber using lasers or highly coherent light from light-emitting diodes (LEDs).
Because a unidirectional ring topology provides only one pathway between any two nodes, unidirectional ring networks may be disrupted by the failure of a single link. A node failure or cable break might isolate every node attached to the ring.